AFSPC-11 is a multi-manifested mission. The forward spacecraft is referred to as CBAS (Continuous Broadcast Augmenting SATCOM) and the aft spacecraft is EAGLE (ESPA Augmented GEO Laboratory Experiment). 1)

CBAS (Continuous Broadcast Augmenting SATCOM)

Managed by the Military Satellite Communications Directorate of the U.S. AFSMC (Air Force's Space and Missile Systems Center), CBAS (Continuous Broadcast Augmenting SATCOM) is a military communications spacecraft destined for geosynchronous orbit to provide communications relay capabilities to support our senior leaders and combatant commanders. The mission of CBAS is to augment existing military satellite communications capabilities and broadcast military data continuously through space-based, satellite communications relay links.

Few details of the CBAS mission have been made public. However, the spacecraft is known to be coordinated by the US Air Force's Military Satellite Communications Directorate, who also manage the operational WGS (Wideband Global Satcom) and AEHF (Advanced Extremely High Frequency) communications programs. The CBAS mass is estimated to be between 2000 and 3000 kg.

EAGLE (ESPA Augmented Geostationary Laboratory Experiment)

Orbital ATK designed EAGLE satellite is the first spacecraft based on the company's ESPAStar platform. The ESPAStar vehicle can accommodate any combination of as many as six hosted or 12 separable, free-flyer payloads in low and geosynchronous orbit and is built to provide an even greater level of access to space. Orbital ATK designed and delivered the EAGLE satellite under a contract with the U.S. AFRL (Air Force Research Laboratory) Space Vehicles Directorate.

On 11 December 2017, Orbital ATK announced that it has been awarded a contract from the U.S. AFSMC (Air Force Space and Missiles Center) to build the LDPE (Long Duration Propulsive Evolved ) ESPA (EELV Secondary Payload Adapter) space platform. The innovative platform, positioned between the launch booster and a primary space vehicle, is used to carry small payloads or deploy small satellites. Under the contract, Orbital ATK will design and manufacture the LDPE using its ESPAStar™ platform. The award includes the initial LDPE, plus options for two additional systems and adds to the rapidly growing production of ESPAStars that support a wide variety of customer missions. 2)

ESPAStar uses a modified EELV Secondary Payload Adapter ring as its structure and is capable of being launched aboard any launch vehicle that meets the EELV (Expendable Launch Vehicle) standard interface specification. It provides a modular, cost effective and highly capable platform for hosting technology development and operational payloads. ESPAStar leverages work performed on the company-designed EAGLE (ESPA Augmented Geostationary Laboratory Experiment), which successfully demonstrated similar technology for the U.S. Air Force. In addition to EAGLE, two ESPAStars are currently in production for other customers.

"ESPAStar's game-changing capability is another example of Orbital ATK's ability to deliver innovative products that fill a need for our customers," said Mike Larkin, Vice President and General Manager for Orbital ATK's Satellite Systems Division. "Based on Orbital ATK's flight-proven GEOStar product line the new ESPAStar technology will provide a cost-effective ride to space for secondary payloads and offers maximum flexibility for orbit locations and deployment."

ESPAStar provides power, propulsion, pointing, telemetry, command and control for attached payloads or for small satellites that can be deployed from the vehicle. Built to provide an even greater level of access to space, Orbital ATK's ESPAStar can accommodate any combination of up to six hosted or 12 separable, free-flyer payloads in low and geosynchronous orbit (Ref. 3).

EAGLE has been built around ESPA, which incorporates the separation mechanism for CBAS. This allows the two satellites to be stacked directly atop each other without the need for an additional payload adaptor such as the SYLDA (SYstème de Lancement Double Ariane, "Ariane Double-Launch System") used on dual-satellite Ariane 5 launches.

The EAGLE ESPAStar spacecraft has a dry mass of 430 to 470 kg with a hydrazine-based monopropellant propulsion system mounted inside the payload adaptor ring with up to 310 kg of fuel. The platform is three-axis stabilized and provides power via a 96 Ahr battery and a deployable solar array, which will generate 1.2 kW of power at the beginning of the satellite's operational life.

On the outside of the ESPAStar platform's adaptor ring, six hardpoints are available to mount payloads. Each hardpoint can accommodate a 181 kg payload , either fixed to the satellite or a deployable subsatellite. EAGLE is the first mission to test the ESPASat bus, which is optimized for geostationary missions but can also be used in other orbits.

The primary mission objective for the EAGLE platform is to demonstrate a maneuverable ESPA-based space vehicle design which can accommodate up to six hosted or deployable payloads in GEO, and can be cost effectively replicated for multiple payload missions to either a GEO, LEO, or GTO orbit.

Launch: The AFSPC-11 mission with the primary payload CBAS and the secondary payload EAGLE was launched on 14 April 2018 (23:13 UTC) on a ULA Atlas-5-551 configuration from the Cape Canaveral Air Force Station SLC-41 (Space Launch Complex-41), FL. — The AFSCPC-11 mission included a second company designed microsatellite, Mycroft, a classified payload which is among several Department of Defense experiments hosted on the EAGLE platform as separate payloads. 3)4)

On 15 April 2018, ULA declared success of the mission in a press release. "Today's launch is a testament to why the ULA team continually serves as our nation's most reliable and successful launch provider for our nation's most critical space assets," said Gary Wentz, ULA vice president of government and commercial programs. "I want to thank the entire ULA team, and the phenomenal teamwork of our mission partners." 5)

The spacecraft are encapsulated in a 5 m diameter short PLF (Payload Fairing). The 5 m PLF is a sandwich composite structure made with a vented aluminum-honeycomb core and graphite-epoxy face sheets. The bisector (two-pieceshell) PLF encapsulates both the Centaur and the satellite. The vehicle's height with the 5 m short PLF is approximately 60 m.

Figure 3: The Atlas 5's RD-180 main engine and five solid rocket boosters propel the rocket off the launch pad into a direct Near-GEO (image credit: ULA)

EAGLE experiments:

EAGLE is a partnership between the AFRL and the STP (Space Test Program) of DoD. It is carrying four fixed experiments and a deployable subsatellite. The fixed experiment packages are (Ref. 3):

• ARMOR (AFRL-1201 Resilient Spacecraft Bus Development Experiment)

• CEASE-III-RR (Compact Environmental Anomaly Sensor III Risk Reduction). CEASE-III-RR will use a suite of instruments to identify conditions in the space environment that could affect the operation of a satellite. Consisting of high and low-energy proton/electron telescopes and an electrostatic analyzer, CEASE will measure the flux of charged particles in geostationary orbit, with this data being used to identify potential causes of anomalies in the spacecraft's data or operation.

• HTI-SpX (Hypertemporal Imaging Space Experiment). HTI-SpX will use a suite of visible-light, ultraviolet and medium and long-wave infrared imagers to collect data that will be used to demonstrate hypertemporal image processing techniques. This will see the satellite collect data over a long period of time, automatically identifying small changes that may warrant further attention. Developed by Raytheon, HTI-SpX will serve as a demonstrator for future long-term surveillance missions.

• ISAL (Inverse Synthetic Aperture LADAR). ISAL will demonstrate laser radar (LADAR) imaging of satellites in geostationary orbit. The payload consists of a synthetic aperture radar system, using the difference in velocity between EAGLE and its imaging target to increase its aperture size for imaging, resulting in higher-resolution images of the target.

The EAGLE experiments will demonstrate enhanced capabilities in space system anomaly resolution and the capability to supplement ground based space situational awareness assets from a geosynchronous platform. EAGLE experiments will also provide new technologies to detect and identify system anomalies such as space weather events and characterize collision events due to micrometeorites.

Mycroft:

The subsatellite, Mycroft, also built by Orbital ATK, will be deployed from EAGLE at an unspecified future date. Mycroft is based around Orbital ATK's ESPASat platform, designed specifically for deployment from the ESPA.

Mycroft is a microsatellite (70 kg) with a payload mass of ~ 30 kg designed to test spacecraft self-inspection techniques. The satellite has a size of 56.6 x 56.6 x 70 cm and has a design life of 3 years. The platform provides three-axis control with six degrees of freedom via reaction wheels and attitude control thrusters. It incorporates a 24 Ahr lithium ion battery with a solar panel generating up to 265 W of power.

The Mycroft goals are to explore ways to enhance space object characterization and navigation capabilities, it will investigate control mechanisms used for flight safety, and it will explore the designs and data processing methods for enhancing space situational awareness.

According to the Air Force fact sheet, Mycroft will fly to a distance of around 35 km from EAGLE, then re-approach the mother satellite to a range of about one kilometer. Mycroft will evaluate the region around the EAGLE minisatellite with an on-board camera, the Air Force said, and use its sensors and software to perform advanced guidance, navigation and control functions.

The information compiled and edited in this article was provided byHerbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (herb.kramer@gmx.net).